They can roost by themselves, but often they can be found in large groups all huddled together in a tree cavity, or hollow. We also stuck plasticine at the entrance to the roosts, so we could look at bite marks and footprints to identify who was visiting, and when. An infrared image of a black rat peeking in an artificial roost. Caragh Threlfall So do bats suffer from high predation rates in our cities?
In biodiversity surveys, bats are often caught using nets and held in small bags for identification. Bat strategies Bats are clever animals though, and may have evolved strategies to evade such attacks. So to investigate what predation pressure bats are under in cities, I decided to take an experimental approach. Safety in bat numbers A currawong investigates an artificial roost. All of the poo produced during such bat surveys was collected and used in my experiment, and I froze it to retain its smell, ready for use. Our results suggest that generalist urban predators may investigate all potential roost sites, making bats very vulnerable to decline, particularly in areas where predator densities are high, such as on islands and in urban environments. To tackle this question, I could have tried to find as many roost sites as possible and monitored how many predators visit and attempt to attack bats at their roosts. An infrared image of a black rat peeking in an artificial roost. Caragh Threlfall I found that common urban species including the black rat and the ringtail possum Pseudocheirus peregrinus were quickly attracted to even small amounts of bat poo. I then set up many artificial bat roosts around patches of urban bushland in Sydney and allowed the animals in the area to get used to the structures for a week. Any animal just curious of my artificial roost would investigate it, and then lose interest after a few days. My study, which was published in Biology Letters last week, explored to what extent native animals living in our cities, namely bats, suffer from predation in patches of urban bushland. Tracy Morris We wanted to test the idea that bats roosting alone, rather than in groups, would not attract as much unwanted attention, and bats switching roosts every day also did not attract as much attention as those that stayed in their roosts for multiple days. Caragh Threlfall So do bats suffer from high predation rates in our cities? And that smell is all the information predators such a black rats Rattus rattus , foxes and cats, need to work out exactly where to sit and wait to prey upon bats. They can roost by themselves, but often they can be found in large groups all huddled together in a tree cavity, or hollow. Going batty Based in Sydney, I found myself attracted to the idea of working on a highly diverse and intriguing group of native mammals - the insect-eating bats. This means that bats roosting alone, rather than in groups, are more vulnerable to predation at their roost. A harp trap, often used in biodiversity surveys. We added bat poo to the roosts every day, and monitored how many potential predators in the area responded to the odour cue by watching them on infrared motion-sensor cameras. None of those projects involve collecting faeces, though. During the time they are in the care of the researcher, they often defecate in their holding bag. You might have seen your cat mimic such behaviour in your own yard, knowing where something to eat is and waiting until the right time to pounce! As you could imagine, large groups of animals all sleeping and defecating in the same place every night makes for a very smelly bed! In addition to this, we found no effect of switching, so bats trying to evade predation by moving roosts every few days may still be found by scent-seeking predators. Caragh Threlfall By odour cues, I mean bat poo - and I needed several kilograms of it in order to run a broad-scale experiment.
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